1. Field of the Invention
This invention relates to an optical lens moving mechanism for zoom lens systems which are used in cameras including video cameras.
2. Description of the Prior Art
Conventional zoom lens systems employ a cylindrical cam having a helical cam groove for moving lenses in the direction of the optical axis of the lenses arranged in parallel to each other. The conventional lens system each comprises at least three coaxial cylinders: a cam cylinder; a fixed cylindrical body; and an operation ring. The cam cylinder is rotatably mounted in the fixed cylindrical body. The operation ring is rotatably mounted to the fixed cylindrical body and rotated by an operator to rotate the cam cylinder. The rotation of the cam cylinder is converted to a linear movement of lens holders holding the lenses so that the lenses move along the common optical axis.
Recently, demand has increased for a zoom lens system which is inexpensive, simple in structure, small in size, and highly precise in lens positioning. However, the conventional zoom lens system cannot fully satisfy the above demand because of the following reasons.
The cam cylinder and the fixed cylindrical body must be machined very precisely for realizing a high precision positioning of each lens, so that the number of parts cannot be reduced much and the machining cost is high. The cam cylinder will be deformed or distorted when a cam groove is formed thereon by cutting. The rotational angle of the cam groove cannot be made large to minimize the distortion of the cam cylinder. Due to the small rotational angle of the cam groove, the cam shift curve is keen, so that the cam movement is not smooth. Also, since the amount of cam movement with respect to the rotated angle of the cam cylinder is great, a small error of the cam causes a large error of the lens movement. Further, the conventional zoom lens system cannot be easily set up due to its complex structure.